DIGESTION 201 



575 cm. or so of the small intestine, and an average meal remains within 

 at least six hours and often twice as long if we include the stay in the 

 stomach. 



The process of "rhythmic segmentation" is well denoted by its name, 

 due to Cannon, who described it from the shadows cast by the digesting 

 intestine of the cat, dog, rat, and rabbit. Bismuth subnitrate having 

 first been mixed with the animals' meals, the chyle was sufficiently opaque 

 to the Rontgen rays, so that its position and condition as regards seg- 

 mentation, etc., could be seen on the fluorescent screen. A cat con- 

 tentedly digesting a meal could thus be studied and watched for hours 

 under more or less normal conditions. Suppose a "string" of chyle 

 10 cm. long contained in a loop of the animal's intestine. Suddenly, by 

 the simultaneous quick constriction of the gut in five or six places, 



FIG. 99 



Lymphatic and Auerbach's plexuses in the intestine's muscular coat: n, the nerve plexus; 

 I, the lymphatic plexus. (Auerbach.) 



this string-like mass of food is cut into as many separate pieces. Two 

 seconds later (in the cat), by intestinal constrictions midway between 

 those which occurred before, these five or six pieces are again divided 

 each in the middle and the halves pushed aside and united again into 

 five or six new pieces. Two seconds later constrictions occur where 

 they occurred four seconds before, thus segmenting the food-mass once 

 more as it was at that time. Thus, the alternate division and uniting and 

 redivision and reuniting goes on thirty times a minute (in case of the cat), 

 perhaps for half an hour or more. The string of chyle meanwhile does 

 not advance along the cat's intestine, but remains to be chopped up by 

 this process of the gut's circular muscular fibers. Wolff corroborates 

 more or less fully these results obtained by Cannon. He thinks the gut's 

 movements are not continuous with those of the antrum, but originate at 

 a point farther down the intestine. In man, probably the rhythm, if it 



